Electronic trigger



4 Sheets-Sheet 1 mnu m @Se c. A. BERGFORS ELECTRONIC TRIGGER May 2, 1950 Filed Dec. 29, 1948 May 2, 1950 c. A. BERGFoRs ELECTRONIC TRIGGER 4 sheets-sheet 2 v Filed Dec. 29, 1948 n n Q s @We ATTORNEY C. A. BERGFORS ELECTRONIC TRIGGER May 2, 1950 4 Sheets-Sheet 5 Filed Dec. 29, 1948 AMA Nm, x. E

BY Q-wm ATTORNEY May 2?'I 1950 c. A. BERGFQRs 2,506,439

I ELECTRONIC TRIGGER Filed Dec. 29, 1948 4 sheets-sheet 4 my er lbattpff g ATTORNEY Patented May 2, 1950 UNITE-o sTAT-Es am o-F'FICE 2,506,439 iitEoTRoNIo TRIGGER CarleLf/Bexgfors, Yonkers, NQY., assigner tolternational Business Machines Corporation, -New York, Ne Y., avcorporation of New York iplilicittlonD'ecelnber 29, 19481,Seria1Nor'675885 (Cl. Z50-2*?) 3 Glaims. 1,

Thisfinv'entionxrelate's to trigger-circuits and lmore particularly-to aehig'hspee'tttrigger of the dual=tube typerhaving :twofconditions of stability.

-n trigger circuits of 'the conventional dual:- tube ty-.1:)e,` the` platefofw-each vtube yis connected to the controlgridof the otherv tube.. Insuoh triggerSyone/of; the chief Alimiting factors aiecting the upperoperating speed lisftheseli-loading-v due to thecross-iconnectedplatesfand grids.

Brieily, theinventionfemploysfour tubes inicluding rtwo tubesused as triggers and two "as cathode followers.- Forthefpurposeof clarity of description, the formerk are referred lto herein as, trigger tubes,l Aand the latter as cathode-follower tubes; Y lower vtube are `interposed between theVV platexof each trigger tube and `the @grid of the.othe1f-tri-g` gel-tube and vice versa.v

Accordingly, Ait is a. principal object of this invention to prov-ide a 'novel trigger wherein-,the trigger performance is relatively unaffected by loading.

Another object -is tov provide aV novel trigger of extremely high operating speed and lowcurrent consumption comprisingycathodefollowers f for cross-coupling the tubesl ofthe trigger.

Still anotherobject is toeprovide a trigger circuit operable over the range-from one cyclenper second to more `thanone megacyole ...per second.

A further object `is to. provide a high speed e trigger operable over a wide rang-e oi supply voltages.

Another object is tov :provide -novel means -for reducing the effect `of input capacitance of. a trigger. l

`Sitiilanother. Objectis try-:providers noi/citric?- 'vger having two. stable. conditions, and using twofgrid controlled tubes with the plate otfcach -eonnected'to the-control grid'of-theotherwherein the time constanty which determines'thetime Certain.-eleotrodes: of one cathode -folf A still further object isto provide a trigger having a pair oi grid controlled tubes with the plate of each connected to the control gridV of the other by means ofva cathode follower.

Still another object is to provide a novel trigger comprising cros'sscoupld tubes, and cathode followersto reduce thefefecty of input capacitance of the grids of the cross-coupled tubes.

vOther objects of thei'nvntion Will be pointedv out the following vdescription and claims and illustrated in the accompanyingidrawingawhich disclose, by way of examples the principle of the invention and the best model, which has been contemplated, fof "applyingy that principle.

`'In the drawings:

Fig. 1 is 'an equivalent circuit diagram of a cathode follower with a pure resistance load;

Fig. 2r isa circuit diagram of oneembodiment of a high speed trigger;

qFig. 4 is a circuit diagram of a further embodiment requiring a fewer number of Voltage supply lines; v l u Fig. 5 is a graph illustrating the Voltage on the 'control grids of 'certain tubes under certain assumed conditions;.and

Fig. 6 is' a vgraph illustrating the voltage `on the control grids vof'certain tubes under 'actual operating conditions.

Throughout the drawings-like Yparts are designated by like numerals.

Before proceedingto 'the description oi the Various embodiments, "itis believed that a brief discussion of various vaspects of a cathode follower circuit i/vill greatly simplify theexplanation of the advahtagesof applicants novel circuits.

Referring to Fig. l, there is illustrated the equivalent circuit diagram of a cathode follower witha pureresistance load.

By a simple mathematical analysis, an expres sion maybe derived for the input capacitance of a cathode follower -in terms of its 'circuit constants. In Fig.` 1, the signal voltage eg is impressed onthe control Ygrid of the tube and the output voltage e'g appears across a cathode resistor Re. lThe voltage between the control grid and cathode is` egx. 'The capacitance between the control grid and cathode is representedlby Cgk and the capacitance between the control grid and plate is represented by Cgp.

It is fundamental that the voltage amplification of any amplifier is the ratio of the output voltage to the input voltage. Therefore, according to the designations of Fig. 1, the voltage arnplication A obtained in a cathode follower is the ratio of the cathode voltage ek to the signal voltage eg or the value of the capacitance C times the voltage E across the capacitor; or

Q=CE (P) It follows that the charge on the control grid Qgk due to the grid-cathode capacitance is expressed by the following equation;

Qgk=Cgkegk (Q) Now, substituting the value of egk of (O) in (Q) Qgk=Cyk(eg-A8g) (R) Also, the charge Qgp due to the grid-plate capacitance is expressed by the following equation;

Qap=carea (S) The total charge Qg on the control grid is equal to the sum of the charges due to the grid-cathode and grid-plate capacitances, hence by adding (R) and (S) Qg=Qgz1+Qgk=Cgpeg+Cgk(ey-Aeg) (T) From (P) the capacitance C, may be written as;

It follows that the effective -input capacitance of Cg is obtained by dividing (T) by eg, hence,

In a similar manner, there may be derived the equation for the input capacitance of a triode amplifier having a pure resistance plate load. This equation is as follows:

Equation V indicates that the input capacitance of the cathode follower, is less than, the sum of the grid-plate and grid-cathode capacitances, by an amount equal to the voltage amplication times the grid-cathode capacitance. The subtraction of the quantity A'Cgg in Equation .V indicates that the cathode voltage is in phase with the signal voltage applied to the control grid of the tube. This means that the feedback voltage through the grid-cathode capacitance is in phase with and tends to sustain the impressed signal voltage. Hence, in the cathode follower circuit, the feedback through the grid-cathode capacitance is equivalent to a reduction in the input capacitance.

On the other hand, Equation W indicates that the input capacitance-of a triode plate-loaded amplifier, is greater than the sum of the gridplate and grid-cathode capacitance by an amount equal to the voltage amplification times the gridplate capacitance. The addition of the quantity (ACgp) indicates that the voltage applied to the control grid is 180 degrees out of phase with the plate voltage. This means that the feedback voltage through the grid-plate capacitance opposes the impressed grid voltage. Hence, in the plate-loaded amplifier circuit, the grid-plate capacitance serves to increase the total input capacitance whereas, in the cathode follower circuit, the grid-cathode capacitance is utilized to decrease the total input capacitance.

In order to more clearly understand the particular advantages obtained from the use of a cathode follower circuit, the values of input capacitances for a triode amplifier and a cathode follower, using the same type of tube, in both cases, will now becomputed and compared.

The grid-cathode capacitance Cgk of a 12AU7 type tube, including the capacitance of the socket, is approximately 1.80 micromicrofarads and the grid-plate capacitance Cgp is approximately 1.75 micromicrofarads. The voltage arnplication A of this 12AU7 tube, when used as a triode amplilier in a conventional trigger circuit is approximately 10, while the measured voltage amplification of this tube, used as a cathode follower, is 0.963. By substituting these values in Equation W the input capacitance Cg of this tube, as a triode plate-loaded amplifier, is found to be 21 micromicrofarads. However, by substituting the above values in Equation V the input capacitance Cg of this tube, used as a cathode follower, is found to be only 1.8 micromicrofarads.

From these computations it is seen that the input capacitance of this tube, as used in the conventional trigger, is almost twelve times that of this same tube, as used in the cathode follower circuit. Hence, by connecting the plates of each trigger tube to the control grids of the cathode follower tubes, respectively, the capacitative load on the plates of the trigger tubes will be decreased by a factor of twelve. Also, since the cathode follower grid is driven only slightly positive with respect to cathode, loading due to grid current is reduced to a negligible quantity.

Further, the resistive component of load coupled to each of the trigger tubes when employed wit a cathode follower is 970,000 ohms as compared with li00,000 ohms when using a conventional trigger. Hence, the plate current loads, which, it is to be noted, are inversely proportional to the resistive components, are in the ratio of 2.4 to 1 between the conventional trigger and the novel cathode follower trigger of applicants device.

lThe effective output impedance of 12AU7 tubes employed as cathode followers, canbe shown to be approximately 360 ohms and since it is only 360 ohms, it is obvious that the trigger grids, `although presenting relatively heavy loading, can easily be driven from the low impedance source. In other words, the current flowing in the cathode follower from its plate to cathode automatically adjusts itself to provide a substantially constant value of output voltage, notwithstandingthe load presented by the control grid of the trigger tube.

Another important advantage of the cathode follower coupled'trigger is that the trigger grids are eectively in parallel with the cathode follower tube cathodes. Thus .the effective time 'constant of the trigger tube grid circuit is redutced permitting operation at higher pulsing ra es. i Y

...New rezerringimore oartioulmrlvaof=m-f2nthe novel trigger .device las shown, -tor -fexample ias: comprising trigger` tubes I I ardcathode follower-:tubes I2 :and .13. vvThese tubesare'actuaily'sectionsnof s-ai12A`U7 miniature twin triade f type-tube but will referredto herein,- as tubes, to? facilitate' the description.

'The :cati'ioeles-iof the tubes f1.0-2- and "'ifI `:aref conF nectedwthrough conductors I4 and 2l5,1'respec tively, .to azero volt linen. The 4plates of .the

tubes :|10 i and JI .I 'f are...connectedVV through: resistors Ili'andl I.8 respectively, each .$120,000 ohms and also through aSresi-stor :IB off `15,000Lohms to Iaphie 25.0 volt linell.

.The platesofthe.oathode'follower tubes lil-and i3 are connected -to the :plus 250 'voit vrlline In through conductors v2l anda-2, respectively, :and

vtheir .cathodes are :oonnectedito the zero'wo'ltline to the junction, of the'resis'tors y-Il land -I'lvvith i -the 'resistor I9. "The output termin-aldil vis coupled through a-capacitor 4I 650500025 l`mio-rofarad-and a-conduetor142`to thecathode-of I3. The-grid oftiibe F0islconnectedbyresistors speetively to the min-us -2^50 volt l'line 32. The cathode oftube I2 iis connected to the 'oon-trol grid of ltube I0 through a resistorlt of 361,000 ohms connected Lto 'the junction of fresistors and 44. Similarlythe control 'grid of' tube II "is `connected through resistors "'4-'6 'and 41 of T2000() vvand '240,000 ohms, respectively, to the minus 3250 voltline 32. 'The 'cathode of 'tube If'3-i's'conneoted to the control 4grid-of -tube I'I through ares'i'stor v48 of 36,000 ohms connected ltoi'the ijunction 'of the resistors 46 and: 4:1.

lWhile no -reset =means are shown, l'it-is '-to"-be understood that such may be Iprovided l-i-n any 'conventional manner and-in accordance with the particular use to which thetrigger is to ybe2-put'. -The trigger, as'illustrated, 'when energized, virili assume', v'by- `:ha-nce z,one 'of its two's'tab'le cond-i'- tions. "For the purposesfoi*explanation,'itlisas.w

sumedthat tubes loandffzfarefinieiauymonsoon, 'ductive yand'tutes #H and 13 conductive. 'This vinitial 'stable condition is 'referred Vto v'helfe-in as the on condition. 'Whelntubes vI0 and ft2, bez- 'come conductive, and tub'esIPI rand" I '3 non-leone -ductive, the triggerislin-i'ts otherfstablefoohdition, designated Alfie'r'ei'n as the "ofP condition'.

When the trigger 'isf-onf the potential at v'the vplate of tube II is vlow'andis"transferredover the conductor 33 to the resistors 34 and 36. consequentl low Vpotential present 'at the .junction oft-heo athodeifollowertube42;;oonnected-ztherzeto andislsuicierrt. 'to maintain that vrgrid belowc'utoff. potential thereby rendering tube lznonconductive. Thespotential .atthe cathode of this tube and at the control grid of tube @I0 is determined 'by the-voltage .divider consisting-.0I the resistors vIML #Iii and 44 connected between the zero volt-@line fIB z andzthe =niinus11250 volt line 32. The `voltage-aat 'theoontrolf .grid of tube Iii `isrfsufv- `Ilciently'negative :to hold it'sbelow-cutoff, tothus render it' non-conductive.y The resulting high potential"at"zthe plate of the tube I0 Eis 'trans` ferred'oiver the :conductor-23 to the resistorsf29 and'3i. The consequent high vpotential present attthezfjunctionoflthe resistorsZ-B and 3| is transierred 'to the control grid ofltube I'3, 'oonneetr-id thereto and renders that tubeuconductive. With this cathodefollower tube 1I3 conducting, itscathode-potentia'l is relatively high, as compared to that-of tube I2, and lthe potential transferred 'to the control 'grid'oftube I!! is sucient'to 'keepi't conductive. Thus the trigger'fremains onfu'n til the potential conditions are changed''by'applioation'of'anegativepulse to input terminal-31.

A'lse'ries of negativefpulses"are'applied across theiin'put termi-nal i3?! and Ithe'zero volt line "I-G. These `puls'esare of suicien't amplitude and steep wavefront to "eiect'svvitch-ihg from either on or oif,`-to the other condition. I'lhetrigger --illustrated isnonires'p'onsive to `positive Apulses Aof the same amplitude-as that-of the nega-tive pulses'. While it isY vvshown that switchingof the trigger is obtained bysupply'ing pulses to the plate c'ireu'it of theftrigg'er tubes, such doesv not' constitute partei noveltyfofthis'device. 'It 'is'uhderstood that-'the Etrigger may be switched vby 'applying Vpulses vtothe `control`grids of the'trig'ger tubesor in' any other conventional manner.

Assumingas stated above, that the trigger is om the `first negative pulse applied, over the input `terminal 3l, capacitor 3.8 and line 39 to the junction of the resistors I1 and I8 with the resistorl-Ifi),suddenly Areduces the voltages on the platesoftubes I0 and II. Whenthe voltage on the plate of tube i-I thus momentarily decreases, a negative pulse is transferred over the conductor 3'3f'and theparallel-connecte'dresistor 313 and capacitor 35, to lthe 'control 'grid of the cathode follower tube I2 but since this tube is already non-conductive,'this negativepulse hasno feiect.

triggerftube's i0 'and il are both momentarily non-conductive, their 'arroces at this instant are atfhiehpotential causingfthe voltages on the con'- trol'grids ofthe cathode follower-tubes I2 and I3 to rapidly r-is'e exponentially toward a finalvalue.

Whnfthe `voltage on the control grid, of the t originally hon-Conductive tube '52, starts its eX;-

ponen-tial rise, it'star-ts from a value ofminus 40 volts and, if 'allowed to continue, would reach a value of approiiimately aplus 87 volts. At the saxneitime, the voltage on the control grid ci the originally 'codiictiveftube LI 3 is fplus "40 volts Vaifizl if allowed to continue to rise would reach a value of plus 60 volts. In other words the voltage differential of the control grid f tube I2 is 127 volts while that of tube I3 is only 2O volts. This is vshown clearly from inspection of Fig. wherein the dotted line curve A represents the voltage on the control grid of tube I2 starting from minus 40 volts while the dotted line curve B represents the voltage on the control grid of tube I3 starting from plus 40 volts. These curves were traced from an oscilloscope and were obtained by increasing the negative bias voltages on the control grids of the tubes sufficiently to prevent the trigger from switching to its other stable condition in response to input pulses and therefore do not illustrate the actual voltages when the trigger is operating under normal conditions. Hence, as shown by curves A and B, the voltages on the control grids of tubes I2 and I3 are shown as reaching final values of plus 87 volts and plus 60 volts, respectively. These curves are drawn to twice' the scale of the curves actually traced from the oscilloscope.

The initial Values of voltage, when the trigger is on, are shown in Fig. 5. As is seen from curve B, before zero time is reached, the voltage at the control grid of tube I3 is plus 60 volts while, as is seen from curve A, that at the control grid of the tube I2 is minus 20 volts. At

zero time, a twenty volt negative pulse is applied v to the control grids of the tubes I3 and I2 which reduces the voltage at those grids to plus 40 volts and minus 40 volts, respectively. It is seen from Fig. 5, that the curves A and B cross, before either reaches the plus 45 volt line. The 45 volt line represents the cathode follower grid potential when the trigger grid is at cutoff bias. This means that the crossover occurs before either tube Ill or II has become conductive since the voltage on the cathode follower control grids must reach a value of plus 45 volts, to render the trigger tubes conductive.

In actual operation, when the trigger flips, these dotted curves A and B of Fig. 5 are not obtained. This is because of the fact that the first tube which becomes conductive, causes the trigger to assume the stable condition corresponding to the conduction of that tube. Hence, the voltage on the control grid of the conductive cathode follower tube rises to a stable value of plus 60 volts and the voltage on the control grid of the other cathode follower tube decreases to a stable value of minus 20 volts. The solid line curves C and D of Fig. 6 are obtained under actual switching conditions and correspond respectively to the curves A and B, which were obtained when actual switching of the trigger was prevented. The actual voltage on the control grid of tube I2 when switching of the trigger from on to off occurs, is shown by the solid line curve C while the voltage on the control grid of .tube I3 during the same period is shown by the .solid line curve D.

As is seen, the curves showing the voltages on 4the control grids of tubes I2 and I3 during actual operation are approximately the same as when operation was prevented, if we exclude the portions occurring after the curve C crosses line 35. It is seen that the solid curve C ascends beyond the plus 45 volt line, almost immediately after it crosses the solid curve D. The curve B of Fig. 5 having much less slope than the curve A, would cross the plus 45 volt line later in time.

When the curve C ascends beyond the plus 45 volt line, the critical voltage is exceeded and tube I2 is rendered conductive. Hence, under actual nipping conditions, the voltage on the control grid of tube I2 continues to rise, not toward a final value of plus 87 volts as shown by dotted curve A of Fig. 5 but toward a value of plus 60 volts, as is seen from solid curve C of Figure 6. When tube I2 is thus rendered conductive, its cathode voltage increases rapidly, which voltage is transferred over capacitor 26 and resistors 45 and 43 to the control grid of tube I0 to render it conductive. Its plate Voltage decreases sharply and this decreased voltage is transferred over conductor 28 and parallel connected resistor 23 and capacitor 3B, to the control grid of tube I3. This is `seen from curve D representing the voltage on the control grid of tube I3, which declines sharply, as the curve C ascends beyond the plus 45 Volt line. As is seen from curve D, the voltage at the control grid of tube I3 decreases until it reaches a final value of minus 20 volts.

The curves of Fig. 6 showing the voltage on the control grids of the cathode follower tubes I2 and I3 when the trigger is switched from on to off may also be employed to represent the voltage on these control grids when the trigger is switched from olf to on When the trigger is switched from off to on, the voltage on the control grid of tube I2 would be represented by the curves B and D and the voltage on the control grid of tube I3 by the curves A and C.

As set forth mathematically above, the input capacitance of a triode trigger tube is greater than the sum of the grid-cathode and grid-plate capacitance but the input capacitance of the cathode follower tubes I2 and I3 is much less than ths sum of the grid-cathode and grid-plate capacitance. The resulting permissible decrease in the capacitance used between the plates of the trigger tubes and the control grids of the cathode follower tubes means that the RC circuit used in the novel trigger circuit of the invention has a much lower time constant than that used in the conventional trigger. In other words, the switching of the present trigger requires less time and the trigger is therefore capable o1.' higher speed operation. This is graphically represented by the extremely steep slope of the curve C showing the rapid increase of the control grid voltage on the tube which is switched from the non-conductive to the conductive state.

Resuming the detailed operation of the circuit of Fig. 2, when the second negative pulse is applied to the input terminal 31 the voltage on the plates of tubes Ill and I I is again decreased. A negative pulse is transferred from the plate of tube I0 over the conductor 28 and parallel connected, resistor 29 and capacitor 30, to the control grid of the tube I3. However, since tube I3 is now non-conductive, this negative pulse has substantially no effect. At the same time, a negative pulse is transferred from the plate of tube Il over the conductor 33 and parallel connected resistor 34 and capacitor 35, to the control grid of conductive tube I2. This control grid is driven below cutoff and tube I2 rendered nonconductive to produce a steep negative pulse at itsv cathode. This steep negative pulse is transferred over capacitor 23 and resistors 45 and 43 to the control grid of conductive tube IQ so that this control grid is driven beyond c-uto to render tube I0 non-conductive. At this point in the switching of the trigger, as in its switching from the on to the off condition, all four tubes I0, Il, I2 and I3 are non-conductive.

The voltages on the control grids of tubes I2 and 'l3vrlsetowardi-a i-lnalrvalue, under-the-control of their respective RC' circuits. It should .be :noted.that-theinitial andzflnalfvoltage values-lof fthev control grid. of itubefl2 willnow correspond :to those values set'forth above for the control grid of.- tube. I 3, when the triggerwas.'switched -ifrom :the on to the fofficondition, in response tothe `irst negative:pulse-'appliedato1 the input `ternxinail f3.1. Also, the. initial'an'dnal voltage-'values.;of

the'control. 'grida of tube 1,3".Wi1l A'novvcorrespond to those values given for the control grid ofl tube I2; when .the triggerwas switched from the on to the off condition, in response to the first negative-pulseapplie'dlto input terminal 31.

Iii-thev Same. manner as-,that-describedin; C011- nection with tubes I and I2;, when svvitchedrby the first negative pulse, thevoltageon the control grid of tube I3 rises above the critical value andthat tube is renderedconductive. Whentube I3 -becomesconductive, the .voltage onA the: :control grid 'oftube 4I Irisesabove :cutoff and renders it conductive, Ato p1acethetrigger inA theion condition.

Subsequent negative pulses applied across input terminal 31 and zero-volt line I6, cause the trigger .to/switch-from onto oif and vice versa, alternately, as in response to the first and second negative pulses, respectively.

Referring to Fig. 3, the power supply arrangement is different from that used in Fig. 2. The plus 250 volt line of Fig. 2 is replaced by the plus 150 volt line 49 of Fig. 3. The cathodes of tubes I0 and II are still connected to a zero volt line I6v but the tubes I2 and I3 are connected via the resistors 24 and 25, respectively, to a minus 10 volt line 50 while the grids of tubes I2 and I3 are connected via resistors 36 and 3|, respectively, to the minus 150 volt line 5| Further, the cathode of tube I2 is directly connected to the control grid of tube I0 by conductor 52 while the cathode of tube I3 and the control grid of tube I I are similarly connected by the conductor 53.

Referring to Fig. 4, the same circuit as in Fig. 3 is illustrated except that the cathode of tube I2 is connected to the control grid of tube I0 b-y means of a conductor 52 and also a parallel connected resistor 54 and capacitor 55. The cathode of tube I3 is also connected to the control grid of tube II through a conductor 53 and a parallel connected resistor 56 and capacitor 51. Resistors 54 and 56 each have a value of 20,000 ohms and the capacitors 55 `and 51 each have a value of 0.00005 microfarad. Resistors 54 and 56 serve to provide a safe current limit through the control grids of tubes I0 and II, respectively, when these tubes are in a stable conductive condition. The capacitors 55 and 51 provide a low impedance path for the higher order harmonics present in the steep wave front pulses normally transferred from the cathodes of the tubes I2 and I3 to effect switching of the trigger tubes I0 and II.

While the circuit shown in Fig. 2 illustrates one arrangement of the novel high speed trigger of the invention using a minimum number of supply lines, a wide variety of arrangements may be used without departing from the teachings of the invention. For example, in Fig. 4, the minus 10 volt line 50 can be eliminated, cathode resistors 24 and 25 connected to the zero volt line I6 and grid bias resistors connected in series with but intermediate the resistors 54 and 56 and the minus 150 volt line 32. Such will require only two voltage supplies and the voltage dividers, each of which is associated with the cathode of one of the cathode follower tubes and the control sult of the conduction and non-conduction of said` .range-.- of supply: voltages; rltrigger.willi=operatewith plate -supplyvoltage as vvvpressedsuccinc tlyeinthemathematical:discussion above... Also.; r'since the cathodev follower has an extremely. low output: impedance, itis capableb driving vthe :trigger `grid to precisely` reproduce :anywolta-ge variationwapplied 1 to the.; cathodeV folf `slowerugrideven though the cathodefollowerf load isappreciaibla Aisch thectrigger-cangbe operated over a. wide For example, the

mwiassplus liwoltssand gridibias `supply voltage cfzminusuzuiueits. 'Withaplate supply voltage plusA 10.01. voltsuande a, grid bias; supply voltage of minusflld `.voltstl'ie-trigger. was .operated sat1- .isfactorily nptoilSQxmegacycles. The/.maximum :speed-, fofgoperationwas'. .1;6: mc., .using plusm2l0 iandminus v1'07: volts;

Although miniature4 triodee. of the .12AU71 type 'wereiemployed and :particular v values of components were :recited herein, itis to.be understood `:tha`t-.the.inventionissby nomeansdim-itedito such tubes and component values but that any suitable type tube and values of components may be employed without departing from the teachings of the invention.

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to a preferred embodiment, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art, Without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

1. A trigger circuit including first and second trigger tubes alternately conductive and nonconductive and vice versa to represent two stable conditions; plate resistors in the plate circuit of said tubes; a connection from said plate circuit to a source of pulses for effecting a change in the stable condition of said trigger; third and fourth vacuum tubes each having their plates connected directly to a voltage source and their cathodes connected to another voltage source through a resistor in the cathode circuit of each; a resistor and capacitor in parallel between the plate of said first tube and the control grid of said third tube for rendering said third tube conductive when said first tube is non-conductive and rendering said third tube non-conductive when said first tube is conductive; a connection from the cathode of said third tube to the control grid of said second tube for rendering said second tube conductive and non-conductive, respectively, as a result of the conduction and non-conduction .of said third tube, said connection including a resistor and capacitor in parallel; a resistor and capacitor in parallel between the plate of said second tube and the control grid of said fourth tube for rendering said fourth tube conductive when said second tube is non-conductive and rendering said fourth tube non-conductive when said second tube is conductive, and a connection from the cathode of said fourth tube to the control grid of said first tube for rendering said rst tube conductive and noneconductive, respectively, as a re- 11 fourth tube, said connection including a resistor and capacitor in parallel.

2. The circuit of claim 1 including bias resistors connected to the control grids of the tubes.

3. A trigger circuit including first and second trigger tubes alternately conductive and nonconductive and vice versa to represent two stable conditions; a resistor connected at one end to the plate of each tube; a resistor connected to a source of plate supply voltage at one end and at its other end to the other ends of the resistors connected to the plates of the tubes; third and fourth tubes each having their plates connected directly to said source of plate supply voltage; a cathode voltage source connected directly to the cathodes of said trigger tubes and through resistors to the cathodes of the third and fourth tubes; a resistor and capacitor in parallel between the plate of said rst tube and the control grid of said third tube for rendering said third tube conductive when said first tube is non-conductive and rendering said third tube non-conductive when said rst tube is conductive; a, resistor and capacitor in parallel between the plate of said second tube and the control grid of the fourth tube for rendering said fourth tube conductive Number when said second tube is non-conductive and ren dering said fourth tube non-conductive when said second tube is conductive; a capacitive connection from the cathodes of the third and fourth tubes to the control grids of the second and rst tubes, respectively; control grid bias resistors connected from the control grids of said tubes to a source of voltage and a resistive connection from the control grid bias resistors of the first and second tubes to the cathodes of the fourth and third tubes respectively.

CARL A. BERGFORS.

REFERENCES CITED The following references are of record in the `iile of this patent:

UNITED STATES PATENTS Name Date i 2,404,047 Flory et al July 16, 1946 2,441,579 Kenyon May 18, 1948 2,454,815 Levy Nov. 30, 1948 FOREIGN PATENTS Number Country Date 587,940 Great Britain May 9, 1947 

